1. Field of the Invention
The present invention relates to a system for measuring a liquid fuel quantity within a container, and a liquid fuel quantity measurement method employing the measurement system.
2. Description of Related Art
A typical construction machine such as a hydraulic shovel is made up of a traveling substructure for making a movement, and a revolving superstructure for performing operations. In such a construction machine, the traveling substructure contains only traveling devices such as tires and crawlers, while the revolving superstructure contains many devices, such as a working arm, actuators, an engine, a counter weight, a fuel tank, and a controller for controlling various devices, compared with the traveling substructure. Because of this, considering the case where such a construction machine performs operations at urban districts or at narrow sites, there is a strong demand for a reduction in the size and operating radius of the revolving superstructure.
To meet such a demand, there is disclosed a technique of making the revolving superstructure compact, by arranging a fuel tank in the traveling substructure to leave a sufficient margin for the arrangement of various devices provided in the revolving superstructure (e.g., Japanese Utility Model Publication No. Hei 6-18052). In this technique, by arranging the fuel tank and fuel feed pump in the traveling substructure and delivering fuel to the engine provided in the revolving superstructure through a swivel joint, the fuel tank can be removed from the revolving superstructure, and at the same time, the radius of the revolving superstructure can be reduced.
However, in the above-described technique, there is a great difference in height (head) between the fuel tank in the traveling substructure and the engine in the revolving superstructure, and consequently, there is a possibility that the fuel in the fuel feed passageway connecting the fuel tank and the engine will go down to the fuel tank and the fuel supply will be shut off.
There is also disclosed a technique of preventing fuel from going down to a fuel tank, by disposing a fuel feed pump and a check valve in parallel in a fuel feed passageway extending between an engine with a fuel pump and the fuel tank (e.g., Japanese Utility Model No. 2516601). In this technique, when there is no failure in the fuel supply system, fuel is supplied to the engine through the check valve by the fuel pump attached to the engine, without operating the fuel feed pump. Since the check valve prevents fuel from going down, the fuel supply can be prevented from being shut off. On the other hand, when a failure occurs in the fuel supply system and the fuel supply is shut off, the fuel feed pump arranged in parallel with the check valve is operated to forcibly supply fuel to the engine.
None of the above-described patent documents give a description of devices that measure a fuel quantity within a fuel tank, but in the case of typical construction machines, the fuel tank is provided with a float gauge to detect the liquid surface. However, when the fuel tank is tilted, or when the liquid surface is moving, it is difficult to accurately grasp a fuel quantity.
Particularly, when the fuel tank is provided in the traveling substructure of a construction machine, it is often formed into a flat shape because of the physical restriction of the space in which the fuel tank is housed. In this case, the liquid surface tends to change greatly by the tilt of a construction machine, so it is even more difficult to make an accurate measurement.
When the fuel tank is arranged in the traveling substructure, as in the techniques disclosed in the above-described patent documents, a slip ring for connecting float-gauge signal lines (electric wires) at the swivel joint is required in order to transmit information detected by the float gauge to the revolving superstructure. In this case, the structure of the swivel joint between the revolving superstructure and the traveling substructure is complex.
The present invention has been made in view of the circumstances above mentioned. Accordingly, the present invention provides a system that is capable of accurately measuring liquid fuel stored in a container. The present invention also provides a liquid fuel quantity measurement method employing the measurement system.